Psoriasis and the Risk of Pneumonia: A Population-Based Study

December Psoriasis and the Risk of Pneumonia: A Population-Based Study Li-Ting Kao 0 1 6 Cha-Ze Lee 2 6 Shih-Ping Liu 3 6 Ming-Chieh Tsai * 4 5 6 Herng-Ching Lin 1 5 6 0 Graduate Institute of Life Science, National Defense Medical Center , Taipei, Taiwan, 1 Sleep Research Center, Taipei Medical University Hospital , Taipei, Taiwan, 2 Department of Internal Medicine, National Taiwan University Hospital , Taipei, Taiwan, 3 Department of Urology, National Taiwan University Hospital and College of Medicine , Taipei, Taiwan, 4 Division of Gastroenterology, Department of Internal Medicine, Cathay General Hospital , Taipei, Taiwan, 5 School of Health Care Administration, Taipei Medical University , Taipei , Taiwan 6 Editor: James D. Chalmers, University of Dundee , United Kingdom Background: Psoriasis is a prevalent autoimmune disorder. Various studies have reported on the relationship between psoriasis and chronic diseases but very few have explored the association between psoriasis and subsequent acute infection. This retrospective cohort study aimed to compare the risk of pneumonia between subjects with and those without psoriasis. Methods: The medical records of 14,022 patients with psoriasis and 14,022 without psoriasis were obtained from the Taiwan Longitudinal Health Insurance Database 2000. Each patient was followed-up for a three-year period. Cox proportional hazard regressions were performed to compare difference of subsequent pneumonia incidence between subjects with and those without psoriasis. Results: There were 206 (1.47%) subjects with psoriasis and 138 (0.98%) without psoriasis hospitalized for pneumonia. By Cox proportional hazard regressions analysis, the HR (hazard ratio) of pneumonia requiring hospitalization for patients with psoriasis was 1.50 (95% confidence interval [CI]: 1.21-1.86) compared to patients without psoriasis. The adjusted HR was 1.40 (95% CI: 1.12-1.73). The adjusted HR of pneumonia hospitalization for subjects with mild and severe psoriasis was 1.36 (95% CI: 1.09-1.70) and 1.68 (95% CI: 1.12-2.52), respectively, compared to those without psoriasis. Conclusions: Patients with psoriasis have significantly higher incidence of pneumonia compared to those without psoriasis. - Competing Interests: The authors have declared that no competing interests exist. Psoriasis is a chronic skin disorder known to be the most prevalent autoimmune disorder worldwide [1]. In the United States, psoriasis affects more than 2% of adults [2], while the prevalence in Europe varies from 0.6% to 6.5% in different regions [3]. Some literature report that psoriasis may be associated with immune system dysfunction and the production of pro-inflammatory cytokines [4]. These cytokines have been found to be etiologically involved in psoriasis and some common chronic diseases [47]. Various studies have demonstrated the relationship between psoriasis and chronic diseases like metabolic syndrome and chronic obstructive pulmonary disease (COPD) [8, 9]. However, very few have explored the association between psoriasis and acute infection. Pneumonia is defined as an acute infection of the lung parenchyma [10]. It remains one of the leading causes of death and is commonly related with great morbidity, mortality, and utilization of healthcare resources [11, 12]. Recently, one study found a relationship between increased level of baseline proinflammatory cytokines such as TNF-a and IL-6 in the systemic circulation of elderly individuals, and an increased risk of subsequent community-acquired pneumonia requiring hospitalization [13]. It suggests that patients with psoriasis who are always in inflammatory states may have a higher incidence of acute infectious diseases than those without psoriasis. Nevertheless, the studies for this issue remain scant. Two previous studies around the 1990s indicate that patients with psoriasis may have higher risk of viral infections, pneumonia, and sepsis [14, 15]. Another population-based study that included Dutch residents as the study population report that the likelihood of infectious diseases in patients with psoriasis have a two-fold higher risk of infection as the reference group [16]. However, no such studies have ever reported the association between psoriasis and pneumonia based on different psoriasis severities. The aim of this population-based study was to investigate the relationship between psoriasis and subsequent risk of pneumonia. Moreover, this study also explored the risk of pneumonia on patients with varying psoriasis severity compared to the general population. Data for this population-based retrospective cohort study were taken from the Taiwan Longitudinal Health Insurance Database 2000 (LHID2000). Taiwan National Health Insurance (NHI) program, which was initiated in 1995, provides comprehensive and affordable medical care for all its citizens. The LHID2000 contains claims data of 1,000,000 individuals randomly selected from the 2000 Registry of Beneficiaries (n523.72 million) of the Taiwan NHI program. The LHID2000 allows researchers in Taiwan to follow-up all the medical services of these 1,000,000 enrollees since the beginning of Taiwans NHI program. The LHID2000, which was open to the researchers in Taiwan, was available from the NHRI (http://nhird.nhri.org.tw/date_01.html). The high validity of data derived from the Taiwanese NHI program was demonstrated by many researchers and by the Taiwan National Health Research Institute [17, 18]. This study was exempt from full review by the Institutional Review Board of the National Defense Medical Center because the LHID2000 consists of de-identified secondary data released to the public for research purposes. This study did not use informed consent since all data were de-identified secondary data. This study features a study cohort and a comparison cohort. The study cohort included 19,939 subjects who received a first-time diagnosis of psoriasis (ICD-9CM code 696 or 696.1) during an ambulatory care visit between January 2002 and December 2008. The date of the first diagnosis of psoriasis was set as the index date. None of the subjects had ever received a diagnosis of psoriasis prior to the index date. Those who were aged ,18 years (n55,917) were further excluded to limit the subjects to the adult population. As total of 14,022 subjects with psoriasis were finally included as the study cohort. The selection procedures were shown in Fig. 1. The matched comparison cohort (n514,022) (one comparison subject per patient with psoriasis) were also retrieved from the remaining beneficiaries of the LHID2000. This comparison cohort was selected by matching patients with psoriasis in terms of gender, age group (1824, 2534, 3544, 4554, 5564, 65 74, 7584, and $85 years), and year of the index date. For the comparison cohort, the year of the index date was simply a matched year when the comparison subjects had a medical utilization. In addition, for comparison subjects, the date of (...truncated)